1. Technical Field
This disclosure relates to an oscillator that uses, as a temperature detection value, a signal corresponding to a difference between an oscillation output f1 of a first oscillator circuit and an oscillation output f2 of a second oscillator circuit, and reduces an influence caused by temperature characteristics of the oscillation output f1.
2. Description of the Related Art
FIG. 18 illustrates a general constitution of a Temperature Compensated Crystal Oscillator (TCXO), which is an oscillator. Reference numeral 90 denotes a crystal unit, and reference numeral 91 denotes an oscillator circuit. Changing a control voltage, which is supplied from a control voltage generator 93 to a voltage variable capacitance element 92, controls capacitance of the voltage variable capacitance element 92 to adjust an oscillation frequency (output frequency).
Since the frequency of the crystal unit 90 changes depending on the temperature, the control voltage generator 93 corrects a control voltage in response to temperatures detected by a temperature sensor 94. In general, a cubic function is stored in a memory 95 for example, then a frequency corresponding to a temperature detection value is read out based on the cubic function (frequency versus temperature characteristic), which is a function to normalize frequency versus temperature characteristics of the crystal unit 90 using a reference temperature. That is, a difference between a frequency at a temperature at that moment and a frequency at the reference temperature is read out. A control voltage that corresponds to the difference between the frequencies is set as a temperature compensation amount. Then, the temperature compensation amount is subtracted from a control voltage that corresponds to the frequency at the reference temperature. Besides an example described above, another oscillator that can output more precise signal is offered. This oscillator uses, as a temperature detection value, a signal corresponding to a difference between an oscillation output f1 of a first oscillator circuit and an oscillation output f2 of a second oscillator circuit to achieve such a precise output. The details thereof will be described in this embodiment.
Incidentally, an oscillator should be adjusted in order to achieve a stable oscillation output. In the example of the TCXO, a function is set, which function determines a control voltage corresponding to the above-described temperature detection value. It is, however, required to make an oscillator connectable to, for example, a device that measures a frequency for adjustment in order to perform such an adjustment without complicating a configuration of an oscillator.
FIGS. 2 and 3 in Japanese Unexamined Patent Application Publication No. 2001-292030 (hereinafter referred to as Patent Literature 1) illustrates a configuration of two crystal units (crystal resonators) sharing a common crystal element on which two pairs of electrodes are disposed. According to the paragraph 0018 in the Patent Literature 1, a frequency difference between the two crystal units is caused by temperature change, accordingly the temperature can be measured by measuring this frequency difference. A relation between this frequency difference Δf and a frequency amount to be corrected is stored in a ROM, and the frequency correction amount is read out based on the frequency difference Δf. This apparatus, however, cannot solve the above-described problem.
This disclosure has been made in view of these circumstances, and an object of the disclosure is to provide an oscillator that can reduce an influence caused by temperature characteristics at high accuracy with simplifying the configuration of the oscillator.